Acceleration sensors can be structured as micromechanical systems. Such sensors are used, for example, in motor vehicles where passenger protection devices (airbag, belt tightener, etc.) or driver assist systems (brake assist for stopping on a slope) evaluate an acceleration signal. One design of such micromechanical acceleration sensors determines an acceleration acting perpendicularly to a substrate with the aid of a rocker-like mass structure. The mass structure is situated tiltably in relation to the substrate about an axis of rotation running parallel to the substrate. A torsion spring holds the mass structure parallel to the substrate in its resting position. Two lever arms of the mass structure which are diametrically opposed with respect to the axis of rotation have varying lengths, so that a center of gravity of the mass structure is outside of the axis of rotation. If an acceleration acts on the rocker-like mass structure perpendicular to the substrate, the center of gravity is deflected against the force of the torsion springs, so that one lever arm tilts toward the substrate and the other tilts away from the substrate.
Normally, electrodes are provided on the substrate under the mass structure, the electrodes together with the mass structure being connected to capacitors. If a distance between one electrode and the mass structure changes, the capacitance of the capacitor also changes. The capacitance is determined and an acceleration signal is provided based on it.
Such micromechanical systems are described in European Patent Application No. EP 0244581 or European Patent No. EP 0773443.
By design, a maximum acceleration that may be recorded using such a micromechanical system is limited to a value that does not yet deflect the mass structure to such an extent that one of the lever arms contacts an electrode or the substrate. The micromechanical system is not able to quantify accelerations exceeding this value, so that they are “cut off” in the resulting acceleration signal. The smallest acceleration at which this effect occurs is called the clipping acceleration.
An object of the present invention is to provide an improved micromechanical system.